Abstract
The goal of this work was to investigate stability in relation to the magnitude and direction of forces applied by the hand. The endpoint stiffness and joint stiffness of the arm were measured during a postural task in which subjects exerted up to 30% maximum voluntary force in each of four directions while controlling the position of the hand. All four coefficients of the joint stiffness matrix were found to vary linearly with both elbow and shoulder torque. This contrasts with the results of a previous study, which employed a force control task and concluded that the joint stiffness coefficients varied linearly with either shoulder or elbow torque but not both. Joint stiffness was transformed into endpoint stiffness to compare the effect on stability as endpoint force increased. When the joint stiffness coefficients were modeled as varying with the net torque at only one joint, as in the previous study, we found that hand position became unstable if endpoint force exceeded about 22 N in a specific direction. This did not occur when the joint stiffness coefficients were modeled as varying with the net torque at both joints, as in the present study. Rather, hand position became increasingly more stable as endpoint force increased for all directions of applied force. Our analysis suggests that co-contraction of biarticular muscles was primarily responsible for the increased stability. This clearly demonstrates how the central nervous system can selectively adapt the impedance of the arm in a specific direction to stabilize hand position when the force applied by the hand has a destabilizing effect in that direction.
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References
Adelstein D (1989) A virtual environment system for the study of human arm tremor. PhD Dissertation, M.I.T., Cambridge, MA
Akazawa K, Milner TE, Stein RB (1983) Modulation of reflex EMG and stiffness in response to stretch of human finger muscle. J Neurophysiol 49:16–27
Buchanan TS, Lloyd DG (1995) Muscle activity is different for humans performing static tasks which require force control and position control. Neurosci Lett 194:61–64
Burdet E, Osu R, Franklin DW, Milner TE, Kawato M (2001) The central nervous system stabilizes unstable dynamics by learning optimal impedance. Nature 414:446–449
Cannon SC, Zahalak GI (1982) The mechanical behavior of active human skeletal muscle in small oscillations. J Biomech 15:111–121
Crago PE, Houk JC, Hasan Z (1976) Regulatory actions of human stretch reflex. J Neurophysiol 39:925–935
De Serres SJ, Milner TE (1991) Wrist muscle activation patterns and stiffness associated with stable and unstable mechanical loads. Exp Brain Res 86:451–458
Doemges F, Rack PM (1992a) Changes in the stretch reflex of the human first dorsal interosseous muscle during different tasks. J Physiol 447:563–573
Doemges F, Rack PM (1992b) Task-dependent changes in the response of human wrist joints to mechanical disturbance. J Physiol 447:575–585
Dolan JM, Friedman MB, Nagurka ML (1993) Dynamic and loaded impedance components in the maintenance of human arm posture. IEEE Trans Systems Man Cybern 23:698–709
Flash T, Mussa-Ivaldi F (1990) Human arm stiffness characteristics during the maintenance of posture. Exp Brain Res 82:315–326
Franklin DW, Burdet E, Osu R, Kawato M, Milner TE (2003) Functional significance of stiffness in adaptation of multijoint arm movements in stable and unstable environments. Exp Brain Res 151:145–157
Gomi H, Kawato M (1997) Human arm stiffness and equilibrium-point trajectory during multi-joint movement. Biol Cybern 76:163–171
Gomi H, Osu R (1998) Task-dependent viscoelasticity of human multijoint arm and its spatial characteristics for interaction with environments. J Neurosci 18:8965–8978
Hogan N (1985) The mechanics of multi-joint posture and movement control. Biol Cybern 52:315–331
Hunter IW, Kearney RE (1982) Dynamics of human ankle stiffness: variation with mean ankle torque. J Biomech 15:747–752
Lacquaniti F, Carrozzo M, Borghese NA (1993) Time-varying mechanical behavior of multijointed arm in man. J Neurophysiol 69:1443–1464
McIntyre J, Mussa-Ivaldi FA, Bizzi E (1996) The control of stable postures in the multijoint arm. Exp Brain Res 110:248–264
Milner TE (2002a) Adaptation to destabilizing dynamics by means of muscle co-contraction. Exp Brain Res 143:515–519
Milner TE (2002b) Contribution of geometry and joint stiffness to mechanical stability of the human arm. Exp Brain Res 143:406–416
Mussa-Ivaldi FA, Hogan N, Bizzi E (1985) Neural, mechanical, and geometric factors subserving arm posture in humans. J Neurosci 5:2732–2743
Perreault EJ, Kirsch RF, Crago PE (2001) Effects of voluntary force generation on the elastic components of endpoint stiffness. Exp Brain Res 141:312–323
Perreault EJ, Kirsch RF, Crago PE (2002) Voluntary control of static endpoint stiffness during force regulation tasks. J Neurophysiol 87:2808–2816
Prochazka A, Trend PSJ (1988) Instability in human forearm movements studied with feedback-controlled muscle vibration. J Physiol (Lond) 402:421–442
Smeets JB, Erkelens CJ (1991) Dependence of autogenic and heterogenic stretch reflexes on pre-load activity in the human arm. J Physiol 440:455–465
Stein RB, Kearney RE (1995) Nonlinear behavior of muscle reflexes at the human ankle joint. J Neurophysiol 73:65–72
Tsuji T, Morasso PG, Goto K, Ito K (1995) Human hand impedance characteristics during maintained posture. Biol Cybern 72:475–485
Acknowledgements
This work was supported by a grant from the National Science and Engineering Research Council of Canada. DWF was also supported in part by the Telecommunications Advancement Organization of Japan. We thank Dr. M. J. Grey for his contributions as well as Drs. M. Kawato, E. Burdet, and R. Osu for related discussions.
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Franklin, D.W., Milner, T.E. Adaptive control of stiffness to stabilize hand position with large loads. Exp Brain Res 152, 211–220 (2003). https://doi.org/10.1007/s00221-003-1540-3
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DOI: https://doi.org/10.1007/s00221-003-1540-3